Thermophoto conversion element

ABSTRACT

A base is metal, ceramic, or a complex combining thereof, and has thereon multiple concave-convex patterns that are provided at one or more pitches equal to or less than 2 μm, and a surface part  1   a  of the base  1  is porous.

FIELD

This disclosure relates to a thermophoto conversion element.

BACKGROUND

Since the Industrial Revolution that began in the 18th century, variousindustries have developed. On earth, the amount of fossil fuels consumedhas been increasing. This leads to a situation where discharged carbondioxide gas remains up in the air and it exerts a role as greenhouseeffect gas. On the ground, due to concrete buildings or asphalt roads,cooling actions on the ground have been degraded. For this reason,air-conditioners have been used more and more. As infrared rays due toradiation from concrete and asphalt are absorbed by air and clouds, itis difficult to release energy out of the earth. This results in avicious cycle where an increase in the amount of fossil fuels usedcauses a further increase in greenhouse effect gas (for example, see NonPatent Literature 1). In a current situation, there are no definitetechnologies to decrease temperature of the ground and objects existingthere.

CITATION LIST Non Patent Literature

-   Non Patent Literature 1: Yuki Ogawa, “Measure to prevent global    warming”, Economic Policy Studies, March 2006, No. 2, p. 229 to 247

SUMMARY

A thermophoto conversion element of the present disclosure comprising abase that includes metal, ceramic, or a complex combining thereof, andhas thereon multiple concave and convex patterns that are provided atone or more pitches of equal to or less than 2 μm, each of the concaveand convex patterns being constituted of a concave portion and a convexportion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a perspective view that schematically illustrates athermophoto conversion element A having cavities on a surface of a baseaccording to a first embodiment. (b) is a graph that schematicallyillustrates emission characteristics of the thermophoto conversionelement A illustrated in (a).

FIG. 2 is a perspective view that schematically illustrates athermophoto conversion element B according to a second embodiment in acase where the part for converting heat into light has a three-layerstructure of a metallic layer-a dielectric layer-a metallic layer;

FIG. 3(a) is a perspective view that schematically illustrates athermophoto conversion element C according to a third embodiment where aheat absorbing member is provided under the base included in thethermophoto conversion element A according to the first embodiment. (b)is a perspective view that schematically illustrates a thermophotoconversion element D according to a fourth embodiment where a heatabsorbing member is provided under the base included in the thermophotoconversion element B according to the second embodiment;

FIG. 4(a) illustrates a state where a metallic membrane is interposedbetween the base and the heat absorbing member included in thethermophoto conversion element C according to the third embodimentillustrated in FIG. 3(a). (b) illustrates a state where an adhesionlayer is interposed between the base and the heat absorbing memberincluded in the thermophoto conversion element D according to the fourthembodiment illustrated in FIG. 3(b).

FIG. 5(a) is a perspective view that schematically illustrates athermophoto conversion element E according to a fifth embodiment where aheat generating member with a terminal for external connection isprovided under the thermophoto conversion element A according to thefirst embodiment. (b) is a perspective view that schematicallyillustrates a thermophoto conversion element F according to a sixthembodiment where a heat generating member with a terminal for externalconnection is provided under the thermophoto conversion element Baccording to the second embodiment.

FIG. 6 is an image of the emission characteristics obtained by thethermophoto conversion element E according to the fifth embodiment.

FIG. 7 is an image of the emission characteristics obtained when thebase having the concave and convex pattern with a different pitch isapplied to the thermophoto conversion element E according to the fifthembodiment.

DESCRIPTION OF EMBODIMENTS

FIG. 1(a) is a perspective view that schematically illustrates athermophoto conversion element A having cavities formed by a concave andconvex pattern on a surface of a base according to a first embodiment,(b) is a graph that schematically illustrates emission characteristicsof the thermophoto conversion element A illustrated in (a).

As illustrated in FIG. 1(a), for example, the thermophoto conversionelement A according to the first embodiment has a configuration suchthat a concave and convex pattern 3 having a concave portion 3 a and aconvex portion 3 b is provided at a pitch P of equal to or less than 2μm on a surface part 1 a of a base 1 that is a hexahedron. Specifically,in the thermophoto conversion element A, the concave and convex pattern3 is formed by forming the concave portion 3 a with a predeterminedinterval on the upper surface side of the base 1. In the base 1, thesurface part 1 a including the top surface and the four side surfacesforming at least the concave portion 3 a is porous. In this case,porosity means that a part has a porosity of equal to or more than 1%.The surface part 1 a of the base 1 refers to an area where a part withporosity of equal to or more than 1% is formed with substantially acertain thickness on the surface of the base 1. Hereafter, the part issometimes referred to as a porous layer. Parts other than the porouslayer have a porosity of equal to or less than 0.8%.

With the thermophoto conversion element A, when the base 1 receivesheat, the concave and convex pattern 3 converts the heat into light at aspecific wavelength (e.g., a wavelength of 10 μm) as illustrated in FIG.1(b), and it is emitted upward with desired directional characteristics.

The effect of the thermophoto conversion element A is explained by usingFIG. 1(b). In FIG. 1(b), the horizontal axis represents a wavelength,the vertical axis on the left side represents the amount of changes inenergy of radiation, and the vertical axis on the right side representschanges in emissivity. The emitted spectrum (reference mark S) indicatedby a dashed line in FIG. 1(b) is changes in energy of a typical objectwithout any limitation on emission wavelengths.

In the thermophoto conversion element A, the top surface of the base 1,which is a hexahedron, has a concave and convex structure as describedabove; therefore, the emitted spectrum (reference mark S2) is obtainedwhich has a form such that a spectrum part (here, reference mark S1)based on black-body radiation is reduced from the emitted spectrum (thereference mark S) of a typical object. Thus, the wavelength of lightemitted is limited, and high emissivity (reference mark Em) is exhibitedwithin a range of the specific wavelength.

Typically, most of infrared rays due to radiation that occurs from heatthat remains on the ground or objects existing there are absorbed byclouds and water up in the air and therefore they stay near the ground.However, if the emitted spectrum of an object is like the spectrum S2illustrated in FIG. 1(b) where it is limited to a range of the specificwavelength that is not absorbed by clouds and water, the heat remainingon the ground or objects existing on the ground may be released highfrom the ground.

In this case, as the surface part 1 a of the base 1 is porous, the base1 is unlikely to release heat due to convection and heat transfer. Thus,it is possible to improve an efficiency of conversion from heat receivedby the base 1 into light.

The reason why the surface part 1 a of the base 1 has a low heat releaseperformance due to porosity is that the size of pores (the maximumdimension (diameter) of open pores) forming the porous layer is small,equal to or less than 10 nm. It is because most (equal to or more than90%) of the microscopic pores are located with an interval of equal toor more than twice and equal to or less than five times the maximumdimension. Therefore, heat is unlikely to be released from the poresforming the porous layer. It is considered that the large number ofpores function as a heat-insulating layer in the surface part 1 a of thebase 1. In this case, it is preferable that the thickness of the porouslayer is equal to or more than 5 nm and equal to or less than 30 nm forthe reason that its function as a heat-insulating layer in the surfacepart 1 a may be improved.

FIG. 1(a) illustrates a state where the surface part 1 a of the base 1itself is porous; however, this is not a limitation, and a configurationmay be such that a porous membrane, which is made of different material,is attached to the surface part 1 a of the base 1.

It is preferable that the entire exposed surface of the base 1 is porousfor the reason that heat insulating properties of the base 1 may beimproved; however, this is not a limitation, and a configuration may besuch that, for example, it is partially provided on the upper surfaceside of the base 1 where the concave portion 3 a is formed.

With the thermophoto conversion element A, the wavelength at which theenergy of radiation exhibits the largest value may be changed byaltering at least one of the pitch P of the concave and convex pattern 3and depth d of the concave portion 3 a.

The reason why the pitch of the concave and convex pattern 3 is equal toor less than 2 μm in the concave and convex pattern 3 is that, dependingon the wavelength of light emitted, the efficiency of conversion fromheat to light is decreased if the pitch is more than that.

The base 1 included in the thermophoto conversion element A ispreferably at least one type of material selected from the groupconsisting of tungsten, molybdenum, silicon carbide, aluminum oxide,ytterbium oxide, and erbium oxide. If a porous layer is attached to thesurface part 1 a of the base 1, it is preferable to use a membrane madeof the same material. The porous layer may include organic resin.

FIG. 2 is a perspective view that schematically illustrates athermophoto conversion element B according to a second embodiment in acase where the part for converting heat into light has a three-layerstructure of a first metallic layer-a dielectric layer-a second metalliclayer. In the thermophoto conversion element B according to the secondembodiment, the base 1 is formed with a three-layer structure of a firstmetallic layer 1A, a dielectric layer 1B, and a second metallic layer1C. The thermophoto conversion element B according to the secondembodiment has a structure such that the second metallic layers 1Cforming the convex portions 3 b are arranged on the upper surface of theflat-plate like dielectric layer 1B. In this case, the gap between thesecond metallic layers 1C is the concave portion 3 a, and the concaveand convex pattern 3 is formed between the dielectric layer 1B and thesecond metallic layer 1C. In other words, the convex portion 3 b isformed by the second metallic layer 1C, and the bottom surface of theconcave portion 3 a is formed by the dielectric layer 1B.

In the thermophoto conversion element B according to the secondembodiment, when the first metallic layer 1A receives heat fromunderneath, the dielectric layer 1B has the effect of enclosing light sothat the heat may be converted into light. In this case, too, it ispreferable that the surface part 1 a of the base 1 is porous.Specifically, it is preferable that, in the thermophoto conversionelement B, the entire exposed surfaces of the first metallic layer 1A,the dielectric layer 1B, and the second metallic layer 1C are porouslayers for the reason that heat insulating properties of the base 1 maybe improved. Thus, in the case of the thermophoto conversion element B,too, thermophoto conversion characteristics are exhibited as illustratedin FIG. 1(b).

FIG. 3(a) is a perspective view that schematically illustrates athermophoto conversion element C according to a third embodiment where aheat absorbing member is provided under the base included in thethermophoto conversion element A according to the first embodiment. (b)is a perspective view that schematically illustrates a thermophotoconversion element D according to a fourth embodiment where a heatabsorbing member is provided under the base included in the thermophotoconversion element B according to the second embodiment.

The thermophoto conversion elements C, D have a configuration such thata heat absorbing member 7 is provided under the base 1, which is thethermophoto conversion element A, B. With this configuration, even if asurface contact between the base 1 and the surface of an installed area(hereafter, sometimes referred to a heated area) is difficult, a surfacecontact between the heat absorbing member 7 and the surface of theheated area is possible. Thus, the base 1 may be provided on a heatedarea in a stable manner. Thus, even if the surface of a heated area hasa complex shape, the thermophoto conversion elements C, D exhibitinghigh thermophoto conversion efficiency may be obtained.

In this case, the material of the heat absorbing member 7 is preferablymetallic material or ceramic because of high heat conductivity. Amongthem, metallic material is preferable in terms of desired workability,easy fitting into shape of the surface of a heated area, and flexibilitywith large areas. The metallic material is preferably the one that hasany of copper, nickel, and iron as its principal component, alloy suchas corrugated galvanised iron or stainless steel, or a combinationthereof.

FIG. 4(a) illustrates a state where a metallic membrane is interposedbetween the base and the heat absorbing member included in thethermophoto conversion element C according to the third embodimentillustrated in FIG. 3(a), and FIG. 4(b) illustrates a state where anadhesion layer is interposed between the base and the heat absorbingmember included in the thermophoto conversion element D according to thefourth embodiment illustrated in FIG. 3(b).

With regard to the thermophoto conversion element C according to thethird embodiment and the thermophoto conversion element D according tothe fourth embodiment, as illustrated in FIG. 4(a)(b), it is preferableto have a configuration such that the base 1 and the heat absorbingmember 7 are attached through an adhesion layer 9. In this case, it ispreferable that the adhesion layer 9 itself is adhesive. With thisconfiguration that the adhesion layer 9 is interposed between the base 1and the heat absorbing member 7, even if both the base 1 and the heatabsorbing member 7 are made of material with a high degree ofelasticity, adhesiveness between the base 1 and the heat absorbingmember 7 may be increased. In this case, it is preferable that thematerial of the adhesion layer 9 is any of metal, metallic oxide, and acomplex material thereof because of an increase in heat conductivity ofthe adhesion layer 9. If they are used as the adhesion layer 9, theirfunctions as the adhesion layer 9 are implemented by adjusting themelting point of these materials. As above, the thermophoto conversionelements A to D illustrated in FIG. 1 to FIG. 4 have a function toconvert heat generated from any object into light at a specificwavelength and emit it.

FIG. 5(a) is a perspective view that schematically illustrates athermophoto conversion element E according to a fifth embodiment where aheat generating member with a terminal for external connection isprovided under the thermophoto conversion element A according to thefirst embodiment. (b) is a perspective view that schematicallyillustrates a thermophoto conversion element F according to a sixthembodiment where a heat generating member with a terminal for externalconnection is provided under the thermophoto conversion element Baccording to the second embodiment. FIG. 6 is an image of the emissioncharacteristics obtained by the thermophoto conversion element Eaccording to the fifth embodiment.

The thermophoto conversion element C according to the third embodimentand the thermophoto conversion element D according to the fourthembodiment illustrated in FIG. 3(a)(b) are provided with the member thatpassively absorbs heat under the base 1 having a thermophoto conversionfunction. In the thermophoto conversion element E according to the fifthembodiment and the thermophoto conversion element F according to thesixth embodiment illustrated in FIG. 5(a)(b), a heat generator 11 aincludes an external terminal 11 b so that it generates heat by itself(here, referred to as a heat generating member 11). The heat generatingmember 11 has a function to increase the temperature of the heatgenerator 11 a due to energy (e.g., electric power) supplied from theexternal terminal 11 b. For example, if the heat generating member 11 isprovided under the base 1 that has a thermophoto conversion function,the heat generated by the heat generating member 11 may be output by thebase 1 as light that has a specific wavelength. In the above-describedthermophoto conversion elements E, F, wavelengths (graphs A, B, C inFIG. 6) at which energy of radiation exhibits the largest value may bechanged by changing output of the heat generating member 11, changingthe pitch P of the concave and convex pattern 3 in the base 1, or thelike.

For example, the resonance wavelength (frequency) of a molecule that isbonded atoms is different depending on the bond distance. Raw ceramiccompacts are used as an example: raw ceramic compacts often containorganic molecules with different molecule chain lengths as well asceramic powder.

If the above raw ceramic compact is degreased, organic molecules aresimultaneously volatilized during a typical heating-type degreasingprocess, and therefore cracks easily occur in the raw ceramic compact.

In such a case, if the thermophoto conversion element E according to thefifth embodiment or the thermophoto conversion element F according tothe sixth embodiment is used during the degreasing process, thewavelength at which energy of radiation exhibits the largest value maybe changed; therefore, in raw ceramic compacts, only a specific organicmolecule may be sequentially volatilized while ceramic powder and otherorganic molecules are prevented from being heated. Thus, it is possibleto prevent the occurrence of cracks in raw ceramic compacts duringdegreasing.

With the thermophoto conversion elements E, F, the rate ofvolatilization of organic constituents from raw ceramic compact may becontrolled. Thus, it is possible to manufacture a degreasing device thatis capable of further reducing the occurrence of cracks. In this case,as the surface part 1 a of the base 1 included in the thermophotoconversion elements E, F is porous, heat transfer (convection) in theair may be prevented. Thus, the thermophoto conversion efficiency of thedegreasing device may be improved.

FIG. 7 is an image of the emission characteristics obtained when thebase having the concave and convex pattern with a different pitch isapplied to the thermophoto conversion element E according to the fifthembodiment. For example, if the base 1 having the concave and convexpattern 3 with the different pitch P is used, output energy of radiationhas peaks P as illustrated in FIG. 7, and organic molecules may besimultaneously oscillated and volatilized.

The thermophoto conversion element is manufactured so as to have aconfiguration illustrated in table 1 and its emission characteristicsare evaluated below. In this case, an alumina ceramic heater including atungsten conductor wire as a resistor body is used as a heat generatingmember. The external size of the alumina ceramic heater is 10 mm×10 mm×3mm in height, width, and depth. The base 1 is manufactured to be 10mm×10 mm×0.1 mm in height, width, and depth. The base 1 including theconcave and convex pattern 3 is manufactured by using a Tungsten platethrough processing according to a laser ablation technique using a mask.The concave and convex pattern 3 is obtained such that the pitch is 1.5μm, the width of the concave portion 1 a is 1.2 μm, the depth of theconcave portion is 1 μm, and the width of the convex portion is 0.3 μm.The surface of the base 1 is subjected to dry etching to form pores 5 awhose average diameter is 10 nm (the depth is also about 10 nm) so as tobe porous.

As for the base 1, the base 1 is manufactured such that the concave andconvex pattern where the pitch is 1.5 μm, the width of the concaveportion 1 a is 1.2 μm, the depth of the concave portion is 1 μm, and thewidth of the convex portion is 0.3 μm and the concave and convex pattern3 where the pitch is 1 μm, the width of the concave portion 1 a is 0.8μm, the depth of the concave portion is 1 μm, and the width of theconvex portion is 0.3 μm are alternately mixed, and they are evaluatedin the same manner (samples where the concave and convex patterns aremixed).

The base 1 including the first metallic layer 1A—the dielectric layer1B—the second metallic layer 1C is manufactured according to asputtering technique by using tungsten for the first metallic layer 1Aand the second metallic layer 1C and SiO₂ for the dielectric layer. Itis manufactured such that the pitch of the second metallic layer 1C is 2μm and the width of the convex portion 3 b of the second metallic layer1C is 1 μm. For the adhesion layer 9, an adhesive (Aron Ceramic:manufactured by Toagosei) including alumina powder is used.

The temperature of the heat generating member 11 for measuring emissioncharacteristics is set so as to reach 600° C. and 900° C. Infraredspectrometers are used for measurement of emission characteristics.

The infrared emissivity of the above samples manufactured is obtainedand, with regard to each of samples No. 1 to 7, it is equal to or morethan 80%, which is higher by equal to or more than 35% than a base witha flat top surface. The infrared emissivity is a value represented as aratio of infrared emission energy to input energy (a unit is watt (W)).Input energy is a value obtained from calculation on the current flowinginto a heater. In this case, energy other than infrared emission energyis released outside the system by heat loss due to convection and heattransfer. Infrared emission energy is measured by using an infraredspectrometer.

TABLE 1 Half-value Temperature of Peak position width of heat of energyof radiation Basic structure of Presence or generating radiation energypeak Sample thermophoto absence of member Wavelength Wavelength No.conversion element adhesion layer (° C.) (μm) (μm) 1 FIG. 5a Absent 6001.5 0.4 2 FIG. 5a Absent 900 1.5 0.2 3 FIG. 5b Absent 900 1.5 0.2 4 FIG.5a Present 900 1.5 0.18 5 FIG. 5b Present 900 1.5 0.18 6 FIG. 5b(Concave and Absent 900 1.3, 1.5 0.5 convex pattern mixed) 7 FIG. 5b(Concave and Present 900 1.3, 1.5 0.45 convex pattern mixed)

As it is obvious from the result in Table 1 that each of the samples(No. 1 to 7) manufactured based on the structure of FIG. 5a or FIG. 5bexhibits emission characteristics. Among them, the samples (the samplesNo. 4, 5, and 7) with the adhesion layer 9 formed between the base 1 andthe heat generating member 11 obtain the same half-value width of energyof radiation as those of the samples (the samples No. 1 to 3 and 6)without the adhesion layer 9.

According to these results, it is understood that the manufactured base1 performs a function to convert heat from a heated object into light ata specific wavelength and emit it. Thus, it is considered that ifbuildings on the ground or asphalt roads are filled with it, the effectof heat release is exhibited.

With the structure of the sample No. 1, a sample with the surface part 1a of the base 1 being dense instead of being porous was manufactured;however, in this case, compared with the sample No. 1, the amount ofheat released from the base 1 is large, and the ratio of energy ofradiation to the amount of heat released is small by about 35%.

REFERENCE SIGNS LIST

-   -   A, B, C, D, E, F THERMOPHOTO CONVERSION ELEMENT    -   1 BASE    -   1 a SURFACE PART    -   1A FIRST METALLIC LAYER    -   1B DIELECTRIC LAYER    -   1C SECOND METALLIC LAYER    -   3 CONCAVE AND CONVEX PATTERN    -   3 a CONCAVE PORTION    -   3 b CONVEX PORTION    -   7 HEAT ABSORBING MEMBER    -   9 ADHESION LAYER    -   11 HEAT GENERATING MEMBER    -   11 a HEAT GENERATOR    -   11 b EXTERNAL TERMINAL

1. A thermophoto conversion element comprising: a base comprising ametal, ceramic, or a combination thereof, and has thereon multipleconcave-convex patterns that are provided at one or more pitches equalto or less than 2 μm, each of the concave-convex patterns comprising aconcave portion and a convex portion, wherein a surface part of the baseis porous.
 2. The thermophoto conversion element according to claim 1,wherein the base comprises a plurality of cavities.
 3. The thermophotoconversion element according to claim 1, wherein the base has athree-layer structure comprising a first metallic layer, a dielectriclayer, and a second metallic layer, the second metallic layer comprisingthe convex portions, and the concave portions formed as gaps between theconvex portions.
 4. The thermophoto conversion element according toclaim 1, wherein a heat absorbing member is arranged on a surface of thebase that is opposed to a surface on which the concave-convex patternsare provided.
 5. The thermophoto conversion element according to claim4, wherein the base and the heat absorbing member are attached by anadhesion layer.
 6. The thermophoto conversion element according to claim1, wherein a heat generating member is arranged on a surface of the basethat is opposed to a surface on which the concave-convex patterns areprovided.
 7. The thermophoto conversion element according to claim 1,wherein the multiple concave-convex patterns are provided at two or morepitches.